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Thermostat housing - coolant leak

When I bought my used 98 VW Jetta, I knew it had a coolant leak. I took it to a mechanic I knew and trusted (my parents’ mechanic - located on the east coast, while I’m on the west) and he told me the leak was coming from the thermostat housing. I didn’t have time for him to fix it, and now it needs to be done. I have very little experience but want to get my hands dirty. Is this something I can fix myself? Are there any good videos/resources that you can suggest on how to replace the thermostat housing?

Hopefully it is a bad gasket and not a cracked housing. You can fix it yourself if your handy and have a set of good quality tools. I’ve had a Craftsman’s set of wrenches and sockets for a couple of decades. my 3/8" ratchet when bad on me recently after 20 years of service, and Sear’s replaced it for free.

For a decent guide with pictures, register at and look at the vehicle repair guides. I’d also suggest you look for a repair book, like Chilton’s or Haynes. They only cost $20, but have a wealth of information to repair and maintain your car. They include pictures and step-by-step instructions.

Also, check online at some auto book stores or even ebay for a factory service manual. This is the gold standard of repair books, and may be less expensive, now that your car is 12 years old. I have one for my 22 year old Toyota Supra, and it covers everything bumper-to-bumper with diagrams and schematics. I also have a Haynes manual, but it’s been collecting dust ever since I found the Toyota Service Repair Manual.

Here’s an outfit that sells discount Haynes Manuals and a link to one for the 98 Jetta (gasoline version).

Replacing a T housing isn’t tough at all. Couple of wrenches, a screwdriver to remove the hose from the housing, a new gasket, small tube of permatex gasket sealant, putty knife and a scraper of some sort is useful to remove the old gasket material. Might as well replace the thermostat while you’re doing it. Back flushing the cooling system isn’t a bad idea either as long as you’re into it but it’s by no means mandatory.

Be careful not overtighten the hold down bolts when reattaching either the old housing or the new one to the head. Chances are the housing is relatively thin cast iron and will crack like a walnut under too much torque. A torque wrench is usful to prevent that mishap but not mandatory. Don’t forget to reattach the hose. Have fun.